[Objectives]  Radar observations were carried out in Gongzhuling, Jilin Province of China in 2015 to confirm the migration dynamics of the third-generation of the armyworm, Mythimna separata, and to analyze the probability of their southward migration. The results provide a scientific basis for forecasting and management of this pest. [Methods]  The migration of third-generation armyworms was investigated based on scanning entomological radar observations, field rearing, field survey trap monitoring and trajectory analysis. [Results]  1. 3^rd generation armyworm moths can reproduce successfully but larval development is delayed. 2. 10.3 times more third generation adults were trapped than first generation adults, and most 3^rd generation moths had undeveloped and unmated ovaries suggesting that they were emigrating from local habitats. 3. Wind direction was basically south, southeast and southwest rather than northeast, which prevented 3^rd generation moths from returning to overwintering regions in southern China. 4. Aerial stratification was observed over three days. Trajectory analysis indicated that most landing areas were restricted to either north of Gongzhuling or North Korea. [Conclusion]  Prevailing southerlies in 2015 prevented local third-generation moths from migrating to overwintering regions. The Pied piper effect made these emigrants incapable of forming a source population of armyworms the following summer.